Recombination within the Y locus in Ascobolus immersus

By A. Kruszewska and W. Gajewski

Vol. 9, No. 2, p. 159 (1967)

In the legend to Fig. 1, p. 165, for ‘(in %)’ on lines 4 and 5 substitute ‘(× 103)’.

Recombination and incompatibility in Schizophyllum

By G. Simchen

Vol. 9, No. 2, p. 195 (1967)

On p. 207, line 9, for ‘½(nα + 1)’ read .

The effective population size is required to predict the rate of inbreeding and loss of genetic variation in wildlife. Since only census population size is normally available, it is critical to know the ratio of effective to actual population size (Ne/N). Published estimates of Ne/N (192 from 102 species) were analysed to identify major variables affecting the ratio, and to obtain a comprehensive estimate of the ratio with all relevant variables included. The five most important variables explaining variation among estimates, in order of importance, were fluctuation in population size, variance in family size, form of N used (adults υ. breeders υ. total size), taxonomic group and unequal sex-ratio. There were no significant effects on the ratio of high υ. low fecundity, demographic υ. genetic methods of estimation, or of overlapping υ. non-overlapping generations when the same variables were included in estimates. Comprehensive estimates of Ne/N (that included the effects of fluctuation in population size, variance in family size and unequal sex-ratio) averaged only 0·10–0·11. Wildlife populations have much smaller effective population sizes than previously recognized.

Genetic similarities among 46 strains of rats based on published data involving 93 samples and 28 biochemical loci were assessed using principal coordinate and cluster analysis techniques. Seventeen strains were represented by more than one colony. In ten of these, nominally identical strains differed, and in four cases this was attributed to genetic contamination. A total of 52 genetically different strains were eventually identified. Strains BN and DA were most dissimilar, while strain BP was the most unusual strain over-all. The principal coordinate and cluster analysis showed three main clusters, which could be explained on the basis of linkage disequilibrium for some of the esterase loci in linkage group 5. Among six of these loci only 12 haplotypes were observed, with 24/52 strains having a single haplotype. Re-analysis of loci in linkage equilibrium failed to reveal any important clusters.

Some sampling properties related with the mean and variance of the number of alleles and single locus heterozygosity are derived to study the effect of variations in mutation rate of selectively neutral alleles. The correlation between single locus heterozygosity and the number of alleles is also derived. Monte Carlo simulation is conducted to examine the effect of stepwise mutations. The relevance of these results in estimating the population parameter, 4Neν, is discussed in connexion with neutralist-selectionist controversy over the maintenance of genetic variability in natural populations.

Mice are the most widely used experimental mammals, and many inbred strains are available. However, except for the relatively recent strains derived from known wild populations, the relationships between wild and laboratory mice are not well understood. Based on the Y-chromosomal restriction fragmentlength polymorphism, seventeen inbred strains were classified into two groups: strains with the Mus musculus musculus type Y chromosome and those with the M. m. domesticus type Y chromosome. We extended the survey to an additional twenty-two inbred strains. The M. m. musculus type Y chromosome was found in AEJ/GnLe, AAU/SsJ, BDP/J, BXSB/MpJ, DA/HuSn, HTG/GoSfSn, I/LnJ, LP/J, NZW/LacJ, RIIIS/J, SB/Le, SEA/GnJ, SF/CamEi, SK/CamEi, SM/J, WB/ReJ, WC/ReJ and YBR/Ei, while the M. m. domesticus type Y chromosome was present in BUB/BnJ, MA/MyJ, PL/J and ST/bJ.

Nine enzyme activity variants and one charge variant of liver/erythrocyte pyruvate kinase have been found amongst laboratory and wild mice. Four of the enzyme activity variants were previously reported to be caused by allelic differences in the structural gene, Pk-ls. Analysis of two putative regulatory gene mutations is now reported, both of which map at, or close to, the structural gene on chromosome 3. One of these mutations, in the inbred strain SWR, is tissue specific, affecting enzyme concentration in the liver but not the erythrocyte the other, which arose in a mutation experiment, doubles the enzyme concentration in both tissues. The organization and the nomenclature in the [Pk-1] gene complex are discussed and are compared with the organization of other comprehensively analysed gene complexes in the mouse.

We consider genetic models for the inheritance of the particular colour patterns of silver foxes. The models are evaluated by computation of statistical likelihoods based on observations of related foxes in extended pedigrees. Problems caused by incomplete paternity information are addressed by inferences based on phenotypic observations. The unreliability of subjective evaluations of fur colour also provides difficulty, in particular crossfoxes emerge as being difficult to differentiate. No evidence of linkage between Agouti locus and Extension locus is found in this dataset.

A total of 39 mutants at the grey-3, grey-4 and grey-5 spore colour loci in Sordaria brevicollis have been investigated for conversion pattern by crossing them with wild type and counting aberrant asci. Twenty-one of the mutants were obtained with ICR170 and all showed postmeiotic segregation only rarely (0–8% of the aberrant asci); two showed conversion predominantly to wild type (class A) and the other 19 predominantly to mutant (class B). Six mutants were obtained with ethylmethane sulphonate and one with nitrosoguanidine, and they all showed postmeiotic segregation frequently (14–54% of the aberrant asci) and conversion usually about equally frequently in each direction, though with considerable diversity between mutants (class C). Eleven UV-induced mutants comprised one of class B and ten of class C. There was considerable variation in aberrant ascus frequency between alleles, but conversion pattern seemed to be independent of this frequency.

The recessive lethal T/t-complex haplotype tw75 was isolated from Jena, East Germany, prior to 1973. It was at first thought to be a standard member of the tw5 complementation group because matings of T/tw75 × T/tw5 produced tailless offspring only (Dunn, Bennett & Cookingham, 1973). Cross tests with all other complementation groups and embryological studies have recently been completed, with results demonstrating that tw75 does not complement the members of either the tw5 or the tw1 complementation groups. Histological studies show that compound embryos tw75/tw5 and tw75/tw1 die with symptoms indistinguishable from tw5/tw5 and tw1/tw1 homozygtes respectively. Thus tw75 represents the first confirmed isolation of a t-haplotype that overlaps two complementation groups.

Body-weight and shank length from 2 weeks of age to adult (and from 8 weeks onwards, shank width) have been measured on 154 fowls all hatched on the same date, belonging to two F1 breed crosses: White Leghorn × Rhode Island Red (L × R) and Indian Game × Light Sussex (G × S). After logarithmic transformation the data have first been analysed cross-sectionally (analysis of the age-means for each sex and cross). A longitudinal analysis (fitting a regression line to the data of each individual) has then been made of the approximately linear portions of the curves. The following conclusions are drawn.

(1) Growth in shank length relative to body-weight between 2 and 10 weeks conforms closely to simple allometry. The coefficient of ontogenetic allometry (heter-auxesis), k, is approximately 0·4, being 0·02 higher in L × R than in G × S and 0·05 higher in males than in females. In females k declines (eventually to zero) after 10 weeks; the decline occurs about 4 weeks later in males. For shank width relative to body-weight k is about 0·25.

(2) At a given body-weight males have longer and thicker shanks than females; L × R have longer but thinner shanks than G × S.

(3) Within sexes and crosses there is highly significant individual variation in k, but the allometry lines do not pass, within the limits of error, through any single point. This implies that variation in relative shank length is complex in its ontogenetic origin.

(4) There is no appreciable correlation within sexes and crosses between shank width and shank length at a given body-weight; this implies (as does (2)) that variation is also complex anatomically.

(5) Differences in shape and rate-of-change of shape contribute only a small part of the total variation within sexes and crosses; most is due to differences in general size and general growth rate.

(6) Shank width at a given body-weight is positively correlated with body-weight at a given age (r = + 0·36 within sexes and crosses). This agrees with the finding that the coefficient of static allometry (allomorphosis) for shank width is much higher than the ontogenetic coefficient. For shank length the ontogenetic and static coefficients are approximately the same.

The relations between the quantity of red eye pigment and related pteridine compounds of Drosophila melanogaster have been studied in a variety of genotypes, which include strains selected for high or low pigment content, various derivatives of these lines and also lines in which one or other of the major autosome pairs were represented by homozygous chromosome pairs, derived by random sampling from the base population and also inbred lines. The quantity of red pigment was defined by the optical density when whole heads were extracted in a suitable solvent, while the pteridines were separated by chromatography and their amounts estimated by means of their characteristic fluorescence.

The evidence from selection, inbreeding and chromosome sampling from the base population demonstrated the presence of substantial genetic variation for pigment content and amounts of related pteridines.

The genetic and biochemical properties of the selected lines differed according to the direction of selection. High lines remained heterozygous after many generations of selection and displayed dominance and epistasis in favour of higher pigment content in crosses to the unselected stock. Selection for low pigment content led to fixation of recessive effects, attributable to particular chromosomes. The dominance-recessive relationship in red pigment differences was also applicable to the associated pteridines.

The metabolic pattern in all lines with reduced pigment content is compatible with the assumption of reduced enzyme activity at particular steps of the pathway leading to the drosopterins (red eye pigments). The two steps accessible to study are subject to genetic variation in the base population, while inbreeding or selection for low pigment content leads to genetically fixed alterations at one or other of these steps. The genetic analysis was consistent with the biochemical evidence.

Increase in pigment content above the normal level, either by selection or chance fixation, is accompanied by correlated increase in all the precursors. Several alternatives are possible but it is suggested that this may be due to an increase in early precursors, before the stages which have been altered in the low pigment lines.

Attention is drawn to the similarity in genetic behaviour between pigment content and body size. Particular emphasis is laid on the value of selection as a means of creating biochemical differences which offer a basis for relating biochemical function and genetic behaviour.

Amongst the four common Ha-ras alleles in both controls and cancer patients, we detected the presence of a polymorphic Xho I site associated specifically with the 6·6 and 7·7 kb Bam HI fragments but absent from the 7·1 and 8·2 kb alleles, as recently reported by others. We have extended this study and report here, the consistent appearance of this Xho I site in unusual alleles close in size to the two common alleles of 6·6 and 7·7 kb, in control lymphoblastoid DNA samples in a variety of tumor DNAs. Unusual alleles grouped around the 7·1 and 8·2 kb common alleles on the other hand, did not possess the Xho I site. The consistent presence of the Xho I site polymorphism, in the unusual Ha-ras alleles surrounding the 6·6 and 7·7 kb common alleles and its absence in alleles around the 7·1 and 8·2 kb common alleles, suggests that the unusual ones are derived from the corresponding common alleles to which they are closest in size.

The name zigzag has been given to an inherited behaviour defect in the mouse in which the animals walk with a zigzag motion. It is inherited polygenically. The anatomical defect responsible for the abnormal behaviour was a reduction or absence of the horizontal canals of the inner ear, the reduction consisting of a constriction in the middle of the canal length, rather than a shortening of the canal.

A multienzyme complex for five of the enzymes in the prechorismate portion of the aromatic biosynthetic pathway has been demonstrated in Ustilago violacea, and has previously been reported in U. maydis (Ahmed & Giles, 1969). This complex is similar to that found in Neurospora crassa and other fungi. In U. violacea polyaromatic-requiring mutants show pleiotropic deficiencies for all five of these enzymes, similar to the extreme pleiotropic polar mutants of the arom gene cluster in Neurospora (Giles, Case, Partridge & Ahmed, 1967a; Case & Giles, 1971). This result is interpreted as mutational evidence for an arom gene cluster in U. violacea comparable to that in N. crassa. A second low molecular weight, heat-stable isozyme of dehydroquinase is shown to be present at high (constitutive) levels in U. maydis, as previously indicated by Ahmed & Giles (1969), but this activity is increased to extraordinarily high levels in cells grown in the presence of quinate. In contrast, U. violacea strains do not grow on quinate, have a single, heat-labile dehydroquinase species, and lack activities for other enzymes in the quinate catabolic pathway.

The rates of mitotic recombination at the loci ade3, ade5–7, ade6 and ade8 were approximated by the method of ‘increasing proportion of variants with growth’. The values (per cell generation) were 3·5 × 10−4 for ade8, 1·4 × 10−4 for ade5–7, 4·0 × 10−5 for ade3 and < 2 × 10−6 for ade6. The relative frequencies of mitotic recombination in regions between ade 5–7 and the centromere were different from those obtained with radiation-induced recombinants.

Double cross-overs were detected in a few crosses involving segment ‘29’ mutants of locus ‘14’ in Podospora anserina. The occurrence of such recombination events made it necessary to reconsider the localization of three mutants. Use of an outside marker and the analysis of many other crosses allowed these mutants to be mapped unambiguously. The change in the localization of one of these mutants together with complementation tests on a new mutant leads to the conclusion that the polycistronic unit of transcription contains only four cistrons instead of the five previously thought to exist.

Chromosomal E. coli DNA appears to be sensitive towards in vivo DNA restriction when transformed to a restrictive E. coli recipient. It is therefore concluded that transforming chromosomal donor DNA is present in a double-stranded form immediately after uptake.

Genetic analysis of E. coli transformants, obtained with UV-irradiated donor DNA under conditions that exclude photorepair, show, especially in a uvrB recipient, loss of donor DNA information compared with the situation where DNA was not subjected to UV-irradiation. Similar conclusions were arrived at after genetic analysis of transductants obtained with UV-irradiated particles of the generalized transducing phage P1. The processing in E. coli of DNA after P1 transduction is thus similar to that of transforming DNA. The observations are discussed and a possible explanation based on single-stranded DNA integration is presented in detail.